1. Field of the Invention
The invention relates to a tracheostoma valve adapted to control the flow of air through a tracheostoma comprising a tubular housing having a first end and a second end, said first end being open to be connected to the tracheostoma, a shut-off valve member normally open to allow air flow through the housing from said first end to the ambient atmosphere and closing at a predetermined air flow rate, and a normally closed cough valve member controlling an opening at said second end to open in response to a particular pressure achieved in said housing and to close automatically at reduction of the air pressure.
Due to deceases of different kinds it is sometimes necessary to remove the larynx by surgery and to open a tracheostoma in order that the individual exposed to the surgery can breath. By the removal of the larynx the ability to speak will be lost but can be restored to some extent by means of another surgery wherein a fistula is opened up between trachea and esophagus to pass air to the oral cavity via the fistula. A one-way valve is mounted in the fistula. This valve referred to as a voice prosthesis, allows air to pass from trachea to esophagus but blocks completely flow in the opposite direction. For speech to be generated the tracheostoma must be closed so that air can be pressed from trachea via the voice prosthesis into esophagus the mucous membranes of which are made to vibrate so that speech is produced. The tracheostoma can be closed by covering the tracheostoma with a finger but it is more convenient to use for this purpose a tracheostoma valve of the kind referred to above, which is attached to the neck of the person that has been exposed to tracheostoma surgery, in order to control the connection between trachea and the ambient atmosphere via the tracheostoma. The tracheostoma valve provides a handsfree control of said connection and the following further advantages:
the tracheostoma will not be obstructed by clothing and, therefore, the tracheostoma valve can be carried more discreetly under a shirt or the like;
the body will promote warming and moistening of the inhalation air;
clothes located in front of the tracheostoma valve will not be soaked by humidity and phlegm.
2. Description of the Prior Art
A tracheostoma valve of the kind referred to above is disclosed in EP-B1-0 617 630. In this prior art embodiment the shut-off valve member and the cough valve member are both constructed as pivoted flaps. The flap forming the cough valve member keeps the opening at said second end of the housing normally closed and forms an opening which is normally open but will be closed by the flap forming the shut-off valve member at said predetermined air flow. The flaps are held in the closed and open position, respectively, by permanent magnets. The shut-off valve flap suffers from the drawback that it will not close until the magnet force is lower than the force produced by the air flow at powerful expiration causing big noise when the flap closes against an associated seat. A further disadvantage of this prior art tracheostoma valve is that the proper function thereof is dependent of the position of the person using the valve; the valve functions in a proper way only when the person holds the head in a substantially vertical position because the function of the valve is based partially on gravity.
U.S. Pat. No. 4,582,058 describes a tracheostoma valve wherein the function of the shut-off valve member is controlled by spring bias. According to U.S. Pat. No. 5,059,208 the shut-off valve member comprises a flexible curled membrane of rubber. These prior art tracheostoma valves require a relatively high pressure in the housing for keeping the shut-off valve in the closed position during speech, which means that it may be difficult to terminate a sentence when the expiration air from the lungs is ebbing due to the fact that the shut-off valve is unintentionally opening to early.